I have been following the ClassD-forum for a while but I haven't seen any real info on this topic.

If you take two self-osc-amps and connect them as a bridge then there is no synchronization between the two amp's. There should be a fair chance of getting a lot of noise at the output as a result of inter-modulation.

If the two half's of the bridge is controlled from the same modulator then they would be in sync. But then there's a problem with the feedback as it is pretty complicated to take the feedback from the analog output. Taking the feedback's before the LPF would be easier, but those are out of phase. I can't figure out how this is to be fed back to the modulator?

I've tried to make a bridge that's in sync and with feedback taken before one of the LPF. This works fine but one half of the bridge is running without feedback and this should/could cause a lot of problems.

here is link to the US patent application 20050068121. I think you will find some ideas in there.

Basically, bridged synchronised modules only need good coupling at the switching frequency. With UcD this can be achieved by placing capacitor across the load and also has added benefit of almost eliminating output HF ripple. For feedback before output filter look at provided link. With one modulator you only need to apply fully differential feedback.

I must admit that I don't get it... if I bridge two half-bridges and connect a capacitor across the load the to outputs will be in sync and I only need feedback from one of them?

Jaka: "With one modulator you only need to apply fully differential feedback." Is that a diff feedback before or after the LPF? Before the filter the signal is a fast square wave and I cant See how a diff-amp could be fast enough to process this signal.

After the filters the signal is mostly a sine wave and the a "normal" diff-amp would do the job. I get that part, but then there's the problem with the phase-shift in the filter. Please comment.

I'm trying to simulate the freq-response of the amp with a feedback path after the LPF but that's a real pain in PSpice. Wouldn't it give the same result if a take an ideal op-amp and ad a LPF instead of the Self-Osc-ClassD-amp?

Regards

TroelsM

EDIT: Forgot one thing: I can't see the pics/drawings in the patent-link.. Any ideas?

Cap across load works only with two UcD modules each having it's own modulator. That works because their feedback is taken after the filter.

With one modulator things are no different in full bridge than in half bridge. If you take feedback before output filter you need integrator for the modulator. Just use differential integrator instead of a single sided one.

You are right about the model, but results are accurate up to the one half of the switching frequency (in clocked designs).

A little more accurate model is presented below. It takes bidirectional power flow into account, so it also models power supply pumping in half bridge.

Originally posted by TroelsM
If the two half's of the bridge is controlled from the same modulator then they would be in sync. But then there's a problem with the feedback as it is pretty complicated to take the feedback from the analog output.

I'm sorry but I don't get it. Please see the attached picture.
Circuit 1 is a standard diff. int. but it cannot be used here without some modification. Curcuit 2 is my first idea, but I cant figure out if this is the right way to go?

The "OutputA" and "OutputB" are the feedback's from each side of the bridge before the LPF's.

If anyone could recommend literature about this topic I would be glad.

Originally posted by Kenshin Just Hypex's full bridge ucd idea in technical information on their site?

differential in / differential out power comparator + differential NFB

Exactly. They don't sell such a beast though, but there's enough info on here that you can possible make your own. I made a few sims to that effect. However the half bridge is just as good.

If you wait for others to do for you you'll be waiting a long time, and honestly I don't find IcePower all that impressive, could we for instance expect super symetrical smoking zobel's? Nah thank you.

KM has done excellent work as a scholar, his papers are excellent, but I think IcePower could well be refined, and there hasnt' been anything new from him in awhile, so don't hold your breath.

I think it far more productive to give someone who's interested a little push and a tip here and there, they're likely to produce something long before some commercial fat cat, and even be willing to share with those who've helped them get there, whereas with the commercial fat cat's we're lucky if we can even steal it off a shelf.